1. Field of the Invention
The present invention relates to a multiple power supply system having a plurality of power supplies controlled by a microcomputer.
2. Description of the Related Art
For example, a conventional audio set comprises a plurality of independent sections, e.g., a tuner section and an amplifier section, and has independent power supplies corresponding to these sections.
On the other hand, recently, microcomputers are generally used and electronic equipment is generally systematically controlled by the microcomputers. For example, a power supply monolithic integrated circuit (a system power supply monolithic integrated circuit) is known. The power supply monolithic integrated circuit is a system power supply wherein a decoder for decoding an output signal from a microcomputer and a plurality of stabilizing power supply circuits selectively controlled by the decoder are arranged on a single chip. This system power supply may be used for an audio set.
In this circuit, one of the plurality of power supply circuits is used for a microcomputer power supply. A protective circuit (such as a current limiter) is incorporated in the circuit for detecting an abnormality when a surge voltage is applied to the system power supply or an abnormality occurs in the decoder section or one of the power supply circuits, and for cutting off a bias of the entire system power supply (that is, for controlling the decoder and each power supply circuit in an OFF state).
In the system power supply described above, when the surge voltage is applied, the protective circuit detects this surge voltage and cuts off the bias of the entire system power supply so as to be able to protect the electronic equipment controlled by the microcomputer. When output short-circuiting occurs in one of the plurality of power supply circuits, the protective circuit detects the short-circuiting and cuts off the bias of the entire system power supply so as not to damage other sections.
In the conventional system power supply described above, however, in a control operation of the protective circuit, since the microcomputer power supply is also controlled in an OFF state, an operation of the microcomputer stops and the entire electronic equipment abnormally operates. In order to reset the power supply of the entire system to return to a normal operation state after the abnormal state is canceled, it is necessary to reset the microcomputer.
As described above, in a control operation of the protective circuit, since the conventional power supply monolithic integrated circuit controls the microcomputer power supply in an OFF state, the entire electronic equipment controlled by the microcomputer abnormally operates, resulting in inconvenience.